Electrical Parameters of EHV Lines

Electrical Parameters of EHV Lines

The continuous and short term current carrying capacity dominates the size of conductors for transmission lines upto 220 kV. For EHVAC transmission, corona and radio interference are equally important in adddition to current carrying capacity for selecting the conductor size.

Bundled conductors are used in EHVAC transmission lines which control the voltage gradiant at the surface of the conductor. This helps in reduction of corona loss and radio interference. To reduce the voltage gradiant further, 2 or more subconductors per phase are employed. For 400 kV lines, 2 or 4 subconductors per phase are used while upto 8 subconductors are employed in case of 765 kV EHVAC line.

The conductors are prevented from getting stuck up due to wind forces or electromagnetic induction by heavy currents by installing spacers at intervals of 80-100 m in each span. Bundled conductors are subject to greater ice and wind loadings as compared to single conductors of same cross section, hence requiring stronger towers. The intra bundle spacing of 45 cm is normally used value which is accepted worldwide.

Typical electrical parameters alongwith conductor details and spacings of 400 kV and 765 kV lines are tabulated in the following table.